1. Field of the Invention
The present invention relates to the hydroxylation of phenols and ethers of phenols with hydrogen peroxide, and, more especially, to the hydroxylation of such phenols/phenol ethers with H.sub.2 O.sub.2 in the presence of a catalytically effective amount of at least one alkali or alkaline earth metal salt of a protonic acid, as well as a free protonic acid.
2. Description of the Prior Art
French Patent No. 69/45,467, published under Number 2,071,464, describes a process for hydroxylating phenols and ethers of phenols with hydrogen peroxide in the presence of a strong acid. The most typically used strong acids are sulfuric, para-toluene sulfonic and perchloric.
The process described in the '467 patent is a very important industrial process. However, serious need continues to exist for a catalyst for that reaction which would be less corrosive to the apparatus employed and would provide at least as good yields, as has been reported in the literature.
Thus, published French Patent Application FR 2,489,816 recommends using the silicalites of various metals for such purpose.
And European Patent Application EP-A-0,299,893 offers the use of bridged clays.
Although these methods employing heterogeneous catalysis appear interesting, they do not address such industrial problems as the recycling of the catalyst, its regeneration and the aging thereof.